Inhibiting ozone decomposition



United States Patent INHIBITING OZONE DECOMPOSITION Gerald M. Platz,Champaign, Ill., assignor, by mesne assignments, to Air ReductionCompany, Incorporated,

New York, N.Y., a corporation of New York No Drawing. Originalapplication Sept. 15, 1955, Ser. No. 534,878, now Patent No. 3,400,024,dated Sept. 3, 1968. Divided and this application Apr. 2, 1968, Ser.

Int. Cl. C06c 15/00 U.S. Cl. 252-186 3 Claims ABSTRACT OF THE DISCLOSUREThis invention relates to a stabilized composition consisting of oxygenand ozone and an effective amount of nitrous oxide to inhibitdecomposition of said ozone.

This application is a division of application Ser. No. 534,878, filed onSept. 15, 1955, now Pat. No. 3,400,024.

This invention relates to the storage, handling and utilization of ozoneand more particularly relates to safely increasing concentrations ofozone or to rendering more safe presently utilized concentrations ofozone.

Prior to the present invention, it was determined that a gaseous ozoneconcentration of less than 14.3 volume percent in gaseous oxygen did notdecompose rapidly in a self-sustaining manner when a high voltage sparkwas passed through the ozone-oxygen mixture. This determinationestablished that ozone-in-oxygen concentrations of less than 14.3 volumepercent of ozone at atmospheric temperature and pressure are very safesince the initiatingdecomposition effect produced by a high voltagespark is seldom encountered in ozone handling practices. It was alsodetermined that a gaseous ozone concentration of about 14.3-38 volumepercent decomposed as a selfsustaining low-velocity decomposition wave,if subjected to a spark. Concentrations of 38 to 44 volume percent givea medium velocity decomposition wave or supported deflagration. Above 44volume percent, high velocity detonation fronts were encountered whensparked. Similar considerations exist with reference to liquid mixturesof ozone and oxygen although higher ozone concentrations are permissibledue to the lower energy level at the temperatures involved and theenergy absorption capacity. With respect to a homogeneous liquidozone-oxygen IIllX- ture, it was determined that high velocitydecomposition did not occur when the mixture was subjected to a highvoltage spark if the concentration by weight of the ozone was less thanabout 48% by weight. Thus, as is the case with gaseous ozone-oxygenmixtures, this liquid spark limit (48 weight percent) is considered verysafe since an activating energy input, equivalent to a high voltagespark, will seldom be encountered. It is apparent that any means whichincreases the spark limit will also provide a greater margin of safetyin the handling of ozone at concentrations above the ozone-oxygen sparklimits since the tendency of ozone to decompose will be retarded. Sinceozone has utility as a rocket propellant and since ozone is an excellentoxidant and reagent for chemical reactions, it is desirable that thehazards due to rapid decomposition be minimized and that themaximum-safety concentrations of ozone be increased.

The primary object of the present invention is the provision of meansfor reducing the tendency of ozone to decompose rapidly.

It is a further object to provide means whereby the spark-resistantpercentage of ozone in a given volume can be increased.

The present invention accomplishes the foregoing objects of reducing thetendency of ozone to decompose 3,547,826 Patented Dec. 15, 1970 rapidlyand of increasing the safe ozone concentrations by the addition ofcertain inhibitors to ozone-oxygen mixtures. These inhibitors aredichlorodifluoromethane (CCl F tetrafluoromethane (CF nitrous oxide (N0), and sulfur hexafiuoride (SP For example, when a small amount ofsulfur hexafluoride is added to a gaseous mixture of ozone and oxygenwhich is not resistant to a high voltage spark, the three componentmixture becomes resistant to spark although the ozone exceeds 14.3% byvolume.

All ozone-containing mixtures herein described are devoid ofhydrocarbons or other sensitizing substances and are not contaminated bythe handling apparatus. All references herein to percentages arepercentages at standard temperature (20 C.) and pressure (14.7p.s.i.a.). The oxygen used in tests herein described was purified of anytrace of hydrocarbons in accordance with U.S. Pat. No. 2,700,648, issuedon Jan. 25, 1955 to Thorp et al. The ozone was made from such oxygen anddistilled in order to obtain percent pure ozone. The names Freon 12,etc., hereinafter used, are tradenames for substances produced by the E.I. du Pont de Nemours & Co., Inc.

The above-mentioned inhibitors were discovered after extensive andnumerous tests. The comparison standard which was used in discoveringthe instant inhibitors was the above-mentioned 14.3 volume percent (20.0weight percent) ozone gas in oxygen gas. As above mentioned, this is thehighest concentration of ozone which will not support an initiateddecomposition or will be self-sustaining. Any composition with a higherpercentage of gaseous ozone will self-sustain an initiateddecomposition. This standard was obtained by numerous tests whichinvolved passing a high voltage spark (about 6000 volts) through variedozone-in-oxygen mixtures.

The gas phase test utilized to determine the 14.3 volume percent limitand to determine the inhibiting substances which decreased the tendencyof ozone to decompose basically involved forming the desired gaseousmixture of ozone and oxygen or ozone, oxygen, and/or the inhibitor in asmall explosion chamber, and passing a momentary high voltage sparkbetween closelyspaced tungsten electrodes in the chamber. Mixing of thegases was assured by placing a piece of Dry Ice on the top of thechamber to cause thermal convection of the gases. The compositions ofthe gaseous mixtures were calculated from the initial pressure of ozonewhich was added first and the total final pressures of ozone and oxygenor of ozone and a known mixture of oxygen and/ or inhibitor. The efiectof the spark was determined by the change in pressure as indicated by amanometer and partial or total decomposition, if any, was determinedfrom the pressure variations.

Twenty-some materials were tested and the aforementioned inhibitors werediscovered to be effective as inhibitors. The non-inhibiting substancesranged typically from nitric oxide ,(NO), for example, which reactedviolently upon initial contact with the ozone-oxygen mixture to neutralsubstances 'which exerted no influence on the location of the limit fordecomposition of concentrated ozone-oxygen mixtures. Another type ofsubstance was Freon 22 (CHClF which reacted after initiateddecomposition due to sparking. A fourth class of substances did notresult in reactions upon either initial contact (like NO) or afterinitiated decomposition (like Freon 22) and were not neutral, but thesesubstances did lower the decomposition limit. Argon, krypton and heliumlowered the decomposition limit. The neutral substances or materialswhich exerted no influence were water vapor, carbon dioxide, chlorine,carbon tetrachloride, and nitrogen. Other substances which compared ineffect to nitric oxide are hydrogen sulphide, ammonium, CH CHFperfluorocyclobutane (C F and boron trichloride (BCl Other substanceswhich are similar to Freon 22. in effect are Freon 21 (CHCl F), sulfurdioxide (SO and hydrogen chloride (HCl).

In contrast to the foregoing, the above-mentioned inhibitors were foundto have an inhibiting etfect which permitted an increase in the ozoneconcentration to above 14.3% by volume. Further tests Were made with thepresent inhibitors in order to determine their ranges of effectiveness.In order to do this, the amount of oxygen was decreased to zero quantitywhile the amount of the inhibitor and the amount of the ozone wereincreased.

The highest concentration of ozone in the respective inhibitor which didnot decompose to any degree when subjected to spark is thespark-resistant limit of the particular inhibitor. For example, withsulfur hexafiuoride, a mixture of 25% by volume ozone and 75% by volumesulfur hexafiuoride did not decompose when subjected to sparking.

The shifting of the ozone limit for rapid decomposition due to sparkingis in direct relation to the increasing amount of the inhibitor and thedecreasing amount of oxygen. For example, a 5050 mixture of sulfurhexafluoride (40.2 volume percent) and oxygen (40.2 volume percent)causes the decomposition limit to shift to about 19.6% by volume whichis midway between the standard of 14.3% by volume and 25% by volume, thespark resistant limit for gaseous ozone-sulfur-hexafluoride mixtures.

When the volume percentage of ozone was increased above the spark limitand hence the percentage of the inhibitor was decreased, a range ofpartial decomposition extending to 100% decomposition exists. Forexample, with a mixture of sulfur hexafiuoride and ozone, the ozone canbe increased to 42% by volume before 100% decomposition occurs. Thedegree of partial decomposition between the spark limit (25%) and thetotal decomposition limit (42%) is a straight-line relationship. Forexample, if ozone constitutes 33.5% by volume of a gaseous mixture ofozone and sulfur hexafiuoride, a spark will decompose 50% of the ozone.

The spark-resistant limits and the range of partial decompositionobtained with the instant inhibitors are shown in the following table:

The limit values (third column) are the volume percentages of ozone in amixture of ozone and the respective inhibitors below and at which nodecomposition resulted from a spark. The ranges of partial decompositionshow the volume percentages of ozone in the respective inhibitors fromthe point of no decomposition from sparking through increasingpercentage decomposition to 100% decomposition from sparking. The degreeof partial decomposition between the respective limits and 100%decomposition is a straight-line relationship for all of the inhibitors.

It is to be appreciated that the spark test is an extreme test since, asabove mentioned, an equivalent amount of such rapid energy will seldombe imparted to an ozonecontaining material. As a consequence, when agaseous ozone-ozygen mixture in which the ozone is concentratedsufiiciently as to have tendency to decompose rapidly contains a smallbut effective amount (about by volume) of any of the present inhibitors,the ozone is rendered more stable. Stated differently, the ozone is lesslikely to decompose at a dangerous rate because the inhibitor Willretard the tendency of ozone to decompose when the imparted energy ismuch less than a spark quantity. It is apparent that the presentinhibitors also can be used as a carrier gas for ozone in a process inwhich the ozone is used in a reaction and the carrier gas isrecirculated for admixing with additional ozone.

Since the melting point temperature of Freon 14 is -l84 C.,submerged-spark tests were made on liquid mixtures of ozone, oxygen, andFreon 14. These submerged-spark tests on liquid mixtures of ozone,oxygen, and Freon 14 which mixtures were maintained above -l C.established that a composition by weight percentages of about 55% ozone,39% oxygen, and 6% Freon 14 was not detonated by a high voltage spark.In other words, a minor amount of Freon 14 permitted an increase in theconcentration of ozone in a homogeneous liquid mixture of ozone-oxygento above the established maximum-safety limit of 48 weight percent. Itwas noted that when a small but effective amount of Freon 14 (at leastabout 1% by weight) was added to a homogeneous liquid ozone-oxygencontaining an unstable amount of ozone, the Freon 14 had an inhibitioneffect or reduced the tendency of ozone to decompose rapidly. Thispermits, in the ordinary handling of ozone, an increase in ozoneconcentration to appreciably above 48 weight percent and gives areasonable margin of safety. The temperature of about 180 C. (such as165 C. with a corresponding pressure of 15 p.s.i.g.) is necessarybecause at l83 C., the liquid mixtures of ozone and oxygen when theozone constitutes about 28 to 73% by Weight separate into two layerswith the bottom layer conaining about 72.4% by weight ozone. Thisconcentration exceeds the present safe limit because of the recognizedrelative instability of ozone. The aforementioned liquid mixtures arepreferably made by condensing Freon 14 in liquid oxygen and thencondensing pure ozone in the liquid Freon l4-oxygen.

A study of all of the substances involved in the tests clearly indicatedcertain common characteristics of the materials which are effective asan inhibitor. A basic requirement, of course, is that the inhibitor mustexist in the same phase as the ozone-oxygen mixture. Thus, for thephysical conditions and respective concentrations which are involved, asubstance might be useful as a gas phase inhibitor but would not beuseful as an inhibitor in liquid ozone-oxygen since this particularsubstance might be a solid under the conditions involved. In addition tothe phase characteristic, the present inhibiting substances had nocarbonto-carbon, no multiple, and no carbon-tohydrogen bonding. Alsothese substances were not cyclic in structure and contained no strainedbond angles. Furthermore, a density for the inhibitor as close to thedensity of ozone for the phase (gaseous or liquid) under considerationand a gamma ratio (ratio of specific heats Cp/Cv) for the inhibitor ofless than 1.4 are indicated as necessary.

From the foregoing it is apparent that, when at least about 5% by volumeof one of the inhibitors is added to gaseous mixtures of ozone andoxygen, there results an inhibition of any tendency of the ozone todecompose rapidly.

Thus, when the ozone constitutes more than 14.3% by volume and hence isunstable or sensitive to the input of energy, it is apparent that asmall but effective amount of one of the instant inhibitors provides animproved margin of safety when added before the ozone concentration issensitive to an input of energy.

While the specific embodiments of the invention have been described, itwill be understood that changes may be made by those skilled in the artwithout departing from the invention as set forth in the followingclaims.

I claim:

1. A stabilized composition consisting essentially of 5 oxygen and ozonein Which said ozone is present in an amount of at least 20% by weight ofsaid mixture and a small but effective amount of N 0 to inhibitdecomposition of said ozone.

2. A stabilized composition consisting essentially of oxygen and ozonein accordance with claim 1 and containing at least about 5% by volume ofsaid N 0.

3. A stabilized composition consisting essentially of at least about 20%ozone by weight and at least about 5% by volume of nitrous oxide toinhibit decomposition of said ozone.

6 References Cited UNITED STATES PATENTS 2,962,449 11/1960 Gaines252-186 3,008,902 11/1961 Cook 252-l86 5 LEON D. ROSDOL, PrimaryExaminer I. GLUCK, Assistant Examiner US. Cl. X.R.

